Hominin Evolution - Human Evolution • Aims: • Must be able to outline the main stages of Human evolution. • Should be able to compare and contrast the main hypotheses for Human evolution. • Could be able to discuss the current and possible future evolutionary trends. Human Evolution: a 1960s View • The illustration below was in common usage in the popular press 30 years ago to represent the linear progression from a primitive ape-like ancestor to modern humans. • It is still used in advertising as a visual metaphor for the “idea” of evolution. Evolving lineage with the accumulation of gradual genetic changes under the influence of natural selection Human Evolution: a 1960s View • Predictions According to the Linear Progression Model • The fossil record should consistently show smooth intergradations from one species to the next. • The Actual Evidence Observed in the Fossil Record • Few smooth inter-gradations from one species to the next • Species tend to appear suddenly in the fossil record • The species linger for varying but often very extended periods of time in the fossil record • The species disappear as suddenly as they arrived • They are replaced by other species which might or might not be closely related to them. Human Evolution: a Modern View • The 1st radiation: Early bipedal apes – including the australopithecines. • The 2nd radiation: Involved genus Paranthropus, group of species that exploited low-grade vegetable food sources (nuts, root tubers and seeds) resulting in (megadont) species with very large teeth. • 3rd radiation: Genus Homo, with the habilines and erectines developing a larger brain, diversifying, and dispersing from Africa to other parts of the Old World. • Last radiation: does not involve major evolutionary divergence, reflects dispersal of modern humans worldwide. Megadonts African apes Early Bipedal Apes Diversity Source: Ian Tattersall, The Fossil Trail, Oxford University Press (1995) • Time (millions of years) A modern view of human evolution maintains that it has occurred as a series of adaptive radiations. Human Evolution Timeline 0 Homo sapiens Chimpanzees (Pan) H. heidelbergensis H. neanderthalensis 1 H. erectus H. floresiensis Paranthropus boisei H. antecessor P. robustus H. habilis 2 H. ergaster Au. garhi Millions of Years H. rudolfensis P. aethiopicus 3 Kenyanthropus platyops Au. africanus Australopithecus bahrelghazali 4 5 6 7 Australopithecus anamensis Archaic and Modern Humans: Rapid advances in brain size; suite of new behaviors. Anatomically modern humans emerge from one of the many regional variants. Erectines: Body height of modern proportions. Increasing brain volume. Sophisticated tools are manufactured and used to kill and process small sized game. Australopithecines: Possessed a gracile body form and were probably opportunistic omnivores/scavengers. Habilines: Brain enlargement, first recognizable stone tools, body remains small/slight. 8 Paranthropines: Early hominids specialized for eating a bulky, low-grade vegetarian diet. Developed powerful chewing muscles and a generally robust skull. Early Hominids: Brain size similar to modern chimpanzees, body remains small/slight. Hominid status may be in question. Au. afarensis Ardipithecus ramidus Orrorin tugenensis Sahelanthropus tchadensis The Origin of Modern Humans • There are two theories accounting for the origin of anatomically modern humans (Homo sapiens): Multi-regional Hypothesis Replacement Hypothesis (Out of Africa / Eve Hypotheses) Present Modern Homo sapiens Archaic Homo sapiens Extinction 0.5 mya Gene flow Homo erectus 1.0 mya African origin African origin The Replacement Hypothesis • Also known as the “Out of Africa Hypothesis” and “Eve Hypothesis”. Modern Homo sapiens Present • All modern humans can trace their evolutionary heritage to a single woman via changes in mitochondrial DNA. Archaic Homo sapiens 0.5 mya • This woman, 'Eve', lived about 200 000 years ago in Africa. Homo erectus • The descendants of this population of modern humans dispersed throughout the rest of the world, displacing all other human populations in existence at the time. 1.0 mya African origin The Multiregional Hypothesis • This theory is based largely on the fossil evidence and the anatomical characteristics of modern populations. Modern Homo sapiens Present • • The mitochondrial DNA data can be interpreted in a variety of ways, one of which supports a multi-regional origin of modern humans. Archaic Homo sapiens 0.5 mya Modern human populations can be traced back in the fossil record to about 1 million years ago when Homo erectus first left Africa. Homo erectus 1.0 mya African origin • Continuous gene flow occurred between regional populations. Dispersal of Modern Humans • This map shows a probable origin and dispersal of modern humans throughout the world. • An African origin is almost Skuhl 101 00081 000 ya certain, with south eastern Africa being the most likely region. Qafzeh 120 00092 000 ya Omo 195 000 ya Probable area of origin for modern humans some 200 000 years ago Border Cave 115 000-62 000 ya Klasies River Mouth 120 000-84 000 ya ya = years ago Dispersal of Modern Humans The first modern humans appear in Europe 40 000 35 000 years ago Humans travel to the Americas between 30 00015 000 years ago Cro-Magnon 30 000 ya Earliest dating in East Asia is 67 000 years ago in southern China Skuhl 101 000 81 000 ya Probable area of origin for modern humans some 200 000 years ago Qafzeh 120 000 - 92 000 ya Omo 195 000 ya Polynesia populated progressively 4500 700 years ago Malakunanja II 50 000 ya Lake Mungo 31 000 ya Border Cave 115 000 - 62 000 ya Klasies River Mouth 120 000 - 84 000 ya Australia was first occupied at least 50 000 years ago Human Biological Evolution • Natural selection has acted over generations on inherited phenotypes and as a result changes have occurred in reference to survival and reproduction. • Evidence of this can be seen in: Variation in height, weight, • Physical traits skin colour, hair texture etc Variation in blood type, • Biochemical traits enzyme concentration, hormones etc Variation in tolerance to • Physiological traits foods, temperature, metabolism etc Activity Answer the questions on pages 383 to 391 and 395/6 in the Biozone books. Present and Future Evolution • Over the next few thousand years, human evolution will be influenced by a number of new factors: • • • • • Natural selection pressures may select for beauty, intelligence, body symmetry, disease resistance, and tolerance to pollutants and electromagnetic radiation. Genetic engineering may introduce new and possibly novel genes to add new traits. Gene therapy may replace, remove, or turn off unwanted, perhaps harmful, genes. Nanotechnology may provide a means to tinker with anatomy and physiology at the cellular level to repair or enhance function. Prosthetic enhancements and implants (although not inherited) may extend human performance beyond its present, natural range. Activity Answer the questions on page 400 in the Biozone books.